Most of the current watches and clocks having a quartz crystal utilize a step motor which has a motor coil of small impedance which receives pulses delivered by an integrated electronic circuit comprising a reference oscillator, a frequency divider, a pulse shaper and a power stage. The power stage is generally composed of complementary MOS transistors, i.e. of N-MOS type and P-MOS type. However, transistors of P-MOS type are poorly suited for power use and it is necessary to make them very large in size if one wishes to avoid substantial loss at their terminals. Also, it is known that P-MOS transistors used alone for power supply occupy 30-50% of the total surface area of the integrated circuit. This affects the cost of the circuit, since it is approximately proportional to the square of its surface area. A significant economical saving could be realized if these power transistors of P-MOS type could be eliminated.